Low temperatures, freezing-thawing cycles, and short growing seasons characterize alpine soils. The mattic epipedon, a special diagnostic surface horizon with an intensive root network, is widely distributed in alpine ecosystems. Studies on the soil macropores and roots of the mattic epipedon layer in response to seasonal freezing-thawing processes on the Qinghai–Tibet Plateau are lacking. This study characterized the soil macropores and roots of alpine meadows during the seasonal freezing-thawing process using X-ray computed tomography and revealed the influence of soil macropores and roots structure on water transport in the mattic epipedon layer of the alpine meadows. The results showed that the soil pore distribution was more uniform during the unstable freezing stage (UFP) and the unstable thawing stage (UTP), whereas there was a clear mattic epipedon layer during the completely thawed stage (TP) and the completely frozen stage (FP). Soils in the TP stage had a higher total surface area density (0.1898 mm2 mm−3), length density (225.28 mm mm−3), node density (1,592 no. mm−3), and connectivity (0.3144) of soil macropores than those in the UFP, UTP, and FP stages. In the TP stages, the density, surface area density, branch density, length density, and node density of roots had significant correlations with the macroporosity, surface area density, length density, node density, and tortuosity of soil macropores. In the FP stage, there were no correlations between the root and soil macropore characteristics. Vertical water is expected to move more readily through the mattic epipedon in the TP stage than in the UFP and UTP stages. Roots were the preferential pathways for water transport into the soil layer of the alpine meadow. Therefore, the mattic epipedon is a key layer for water and nutrient storage and plays an important role in the water-holding function of the Tibetan Plateau due to its greater root development.

中文翻译：

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青藏高原东北部青海湖流域高寒草甸季节性冻融过程中土壤大孔隙和根系结构特征及其对水分输送的影响

高山土壤具有低温、冻融循环和生长季节短的特点。基质表层是一种具有密集根系网络的特殊诊断表面层，广泛分布于高山生态系统中。青藏高原土壤大孔隙和基质表层根系对季节性冻融过程响应的研究还缺乏。本研究利用X射线计算机断层扫描技术对季节性冻融过程中高寒草甸土壤大孔隙和根系进行了表征，揭示了土壤大孔隙和根系结构对高寒草甸基质表层水分输送的影响。结果表明，不稳定冻结阶段（UFP）和不稳定融化阶段（UTP）土壤孔隙分布较为均匀，而完全解冻阶段（TP）和完全冷冻阶段（FP）则有清晰的无光泽表层。TP阶段土壤的总表面积密度（0.1898 mm2 mm−3）、长度密度（225.28 mm mm−3）、节点密度（1,592个mm−3）和土壤大孔连通性（0.3144）均高于那些处于UFP、UTP和FP阶段的人。TP阶段根系密度、表面积密度、分枝密度、长度密度、节密度与土壤大孔隙度、表面积密度、长度密度、节密度、迂曲度呈显着相关。在FP阶段，根系与土壤大孔隙特征之间不存在相关性。预计垂直水在 TP 阶段比 UFP 和 UTP 阶段更容易穿过基质表层。根系是将水输送到高寒草甸土层的优先途径。因此，基质表层是水分和养分储存的关键层，由于其根系发达，在青藏高原的持水功能中发挥着重要作用。